This invention relates generally to a downhole apparatus utilized to substantially separate, while downhole, a formation fluid from a subterranean well into constituent portions, and in particular to a downhole separation apparatus for producing and then conveying petroleum products to the well surface separately from undesirable products that are returned to a formation.
Oil and/or gas wells quite often pass through a productive strata whose yield, besides including oil, gas and other valuable products also includes undesirable and unwanted denser constituents such as salt water. In oil well production operations, relatively large quantities of water are frequently produced along with the valuable petroleum products. This is particularly true during the latter stages of the producing life of a well. Handling this water at the surface represents a significant expense in lifting, separation, and disposal.
Various methods have been employed for extracting the valuable petroleum yield from the denser and unwanted constituents. Some have involved the pumping of the total yield to the surface of the well and then using various methods for separating the valuable yield from the unwanted portion of the yield. In addition, the unwanted portion of the yield, after having been pumped to the well surface and separated, has been then pumped downwardly again through a remote well bore into a disposal layer.
In some oil wells, the unwanted denser constituents can amount to as much as 80% to 90% of the total formation yield. Accordingly, to obtain a given volume of valuable petroleum yield from the well, eight or nine times the volume of the valuable yield must first be pumped to the surface of the well and then separated from the unwanted portion of the formation yield. As set forth above, this process can be very slow and expensive. Although the problem of producing substantially water-free oil from a reservoir may occur at any stage in the life of an oil well, the proportion of water to valuable yield generally increases with time as the oil reserves decline. Ultimately, when the lifting costs of the combined petroleum and water constituents exceed the value of the recovered oil, abandonment of the well becomes the only reasonable alternative.
Many procedures have been tried for producing water-free oil from a formation that has a large quantity of water. For example, the oil and water produced are pumped or otherwise flowed together to the surface where they are then treated to separate the petroleum from the water. Since the volume of the water is usually much greater than that of the oil, the separator must handle large volumes of fluid and therefore is large and accordingly expensive. Moreover, the water produced contains mineral salts which are extremely corrosive, particularly in the presence of air. Also, flowing the oil and water together upwardly through the well sometimes forms emulsions that are difficult to break. Such emulsions frequently must be heated in order to separate them even when in the presence of emulsion treating chemicals. The heating of the large amount of water, as well as the small amount of oil, requires an expenditure of large amounts of energy, reducing the net equivalent energy production from the well
Water produced from deep formations within the earth frequently contains large amounts of natural salts. For this reason, the salt water brought to the surface cannot be disposed of by allowing it to flow into surface drains or waterways. Relatively small volumes of salt water can sometimes be disposed of by drainage into a slush pit or evaporation tank. The required disposal method for large volumes of salt water, however, is to introduce the water into a subsurface formation. This requires a disposal well for receiving the produced salt water.
By returning the water to the same formation in this manner, the water is disposed of and also acts more or less as a re-pressurizing medium or drive to aid in maintaining the bottom hole pressure and driving the well fluids toward the producing well. But, in those areas where producing wells are widely separated, the cost of drilling disposal wells for each producing well is prohibitive. In such instances it is necessary to lay a costly pipeline-gathering network to bring all of the produced water to a central location, or alternatively, to transport the produced water by trucks or similar vehicles. Regardless of the method for transporting the waste salt water from a producing well to a disposal well, the cost of the disposal can be, and usually is, prohibitive.
Furthermore, fluids from subterranean reservoirs can have undesirable characteristics such as excessive pressure and being super-heated. If excessive pressure is present, then surface equipment, such as a choke manifold, must be installed to choke the flow pressure down to about 2,000 p.s.i. If a highly pressurized fluid depressurizes within a short amount of time, then a large portion of the gas is xe2x80x9cflashedxe2x80x9d in that a chemical reaction occurs. This reaction adversely affects the desirable petroleum yield from the formation yield. In general, both well seals and surface equipment suffer in the presence of excessive fluid pressure and heat. This equipment is expensive in terms of maintenance and capital costs. Thus, it is highly desirable to minimize these undesirable characteristics of the well flow before being brought to the surface.
Downhole separation has been utilized to a limited extent through the use of hydrocyclones, or combinations of mechanical pumps and gravity separation for achieving separation of production fluids into water and hydrocarbon components. An example of such a device is provided in U.S. Pat. No. 5,857,519, issued Jan. 12, 1999 to Bowlin et al., which recites a method and apparatus for the downhole disposal of a water component of a production fluid while using gas lift techniques to lift the hydrocarbon component. Separation of the water component from the production fluid occurs in the annulus between the well casing string and the well tubing string. The gas lifting technique uses gas lift valves spaced along the length of the casing string for high-pressure injection of gas into the tubing string to lift the hydrocarbon component. Disposal of the water fluids into an underlying formation is provided by a pump mechanism.
But previous devices have been limited to secondary recovery methods in which the natural pressure of a formation is waning. Secondary recovery methods, such as gas lift, or pump jacks, have additional energy requirements for bringing a production yield to the surface. Accordingly, the capacity for these devices to accommodate high production fluid flows is limited, and furthermore, generally requires additional hardware and equipment placed within the bore, restricting the effective inner diameter of a tubing string. A restricted inner diameter affects the ability for routine maintenance of a well below the separation device, as well as upkeep and maintenance of the pumps and hydrocyclones.
Accordingly, a need exists for a downhole separator that separates the valuable yield from a production yield, and that can leave the unwanted portion of the yield downhole. Also needed is a downhole device that can moderate high-pressure and high-temperature characteristics of the production yield. Additionally, a downhole separator is needed for allowing separation of production fluids into constituent portions from the primary recovery lifespan through the secondary and tertiary recovery lifespans of a well.
Provided is a downhole separator that separates the valuable yield from a production yield that can leave the unwanted portion of the yield downhole. The downhole separator of the present invention can also moderate high-pressure and high-temperature characteristics common to primary production flows, as well as provide downhole separation for secondary and tertiary recovery phases of a well lifespan.
An aspect of the present invention is a method for separating a valuable yield from a production fluid. The method provides under-reaming a portion of a well bore such that a separation chamber is defined in a downhole environment, receiving the production fluid in the separation chamber, and quiescently separating the valuable yield from the production fluid in the separation chamber. The valuable yield can then be conveyed from the separation chamber.
Another aspect of the present invention is a downhole separation chamber. The downhole separation chamber has an under-reamed cavity that is defined in the downhole environment about a portion of a well bore. The under-reamed cavity has an interior volume sufficient to quiescently separate a valuable yield from the production fluid, which can be received in the under-reamed cavity.
In a further aspect of the present invention, a downhole separation tool is provided which utilizes a downhole separation chamber with a series of fluid regulators responsive to, a formation fluid and constituent components to separate desirable formation yields from the less desirable yields prior to lifting the fluids to the surface. The separation chamber has an input for the formation fluid, a production output, and a disposal output, in a tree arrangement according to the density order of the fluids in the separation chamber. The input flow regulator is coupled to the separation chamber input, the production regulator is coupled to the production output, and the disposal regulator is coupled to the disposal output. Each of the regulators are responsive to a fluid density of the formation fluid, first constituent and remainder constituent, accordingly, to regulate the flow of the respective fluid.
According to another aspect of the present invention, a method of separating a production fluid downhole is provided where a production fluid is flowed from a subterranean formation into a separation chamber. The production fluid is separated over a given residence time period into a series of constituent layers. The first constituent, such as oil, is lifted in a generally continuous manner when under sufficient pressure to the surface, and the remainder constituent, such as salt water, is disposed to a disposal layer in the subterranean formation.
In yet another aspect of the present invention, if there is insufficient pressure to lift the first constituent toward the surface, a second constituent, such as gas, can be injected into the first constituent to provide a sufficient lifting capacity for the first constituent. In yet a further aspect, the first constituent is injected under pressure into the separation chamber to urge the remainder constituent into the disposal layer.